[84.04] The Population of Weak Mg II Absorbers

J. R. Rigby, C. W. Churchill, J. C. Charlton (Penn State)

We have found 30 weak (0.02 < W_r(2796) < 0.3 ÅMg\kern 0.1em\sc ii absorption systems in an unbiased
survey of 26 quasars over the redshift range
0.4 = 0.9
is dN/dz= 1.7\pm 0.1; thus, they comprise the bulk
(\sim 65%) of all Mg\kern 0.1em\sc ii absorbers.
Fe\kern 0.1em\sc ii was detected in 11 of the systems.
The Fe\kern 0.1em\sc ii to Mg\kern 0.1em\sc ii column
density ratios range from super--solar to below 0.1 solar,
indicating that the \alpha--group to iron--group
enrichment processes are varied among weak
Mg\kern 0.1em\sc ii systems. These weak systems represent
a new population of Mg\kern 0.1em\sc ii absorbers
in that the associated luminous objects they select are
unknown. In contrast, strong Mg\kern 0.1em\sc ii absorbers
(W_r > 0.3 Åare known to select the population
of normal galaxies. Weak Mg\kern 0.1em\sc ii systems may
select some combination of normal galaxy outskirts, ejected
or tidally stripped material, and low surface brightness
galaxies. In particular, those systems with high iron--group
abundances could select out the population of ``giant''
low surface brightness galaxies.

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The author(s) of this abstract have provided an email address for comments about the abstract: jrigby@astro.psu.edu